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I bought this motor with the intentions of rebuilding it, but it was full of gunk water and rust . I’m not sure if it’s salvageable. Any thoughts on its condition? It appears to have never been taken apart based on the original shim gaskets and Teflon coated timing gear . You can barely make out the block stamp but I believe it’s a 70 .
The biggest issue I see is the pitting in the bores. It may or may not clean up when you bore it. Take some 80 grit sand paper and go at one of the cylinder walls till you get to bare metal and then see what it looks like. #3 in your picture looks like the worse one. You cant hurt it and it might give you a better idea if it is worth fooling with.
thanks I will go at it tonight to get a better idea. The machinist said when I’m ready, bring it down and he will visually inspect it to see if it’s worth while to move forward.
I went at it with some 80 grit to me it doesnt look bad i hope it will clean up with a .030 overbore because it is an original low mile motor the bearings in it had very little wear . A shame it was so neglected
i guess i should start another thread on building this motor if it checks out, but ill ask this question here : what made the compression ratio drop from 10.25 :1 on a 70 olds 350 4bbl vs 9:1 on the 70 2bbl? head volume? piston dish size? its considerable drop we know they both have #6 heads the same head gasket same bore and stroke .
i guess i should start another thread on building this motor if it checks out, but ill ask this question here : what made the compression ratio drop from 10.25 :1 on a 70 olds 350 4bbl vs 9:1 on the 70 2bbl? head volume? piston dish size? its considerable drop we know they both have #6 heads the same head gasket same bore and stroke .
Yes, With Oldsmobile the pistons were different for the different compression ratios.
Piston dish as said. The new Mahle 4032 forged and coated 10cc dish piston with a 1mm/1mm/2mm ring pack is really nice the Cutlassefi brought to the market. It will give mid 9 to 1 compression with your #6 iron heads and is available in a 4.100" size. That is a 0.043" overbore and size I went with since a couple of cylinders would not clean up at 4.065". The cast replacement pistons will give you 8 to 1 compression at best, very short on compression height. The Speedpro forged are made in India and need twice the piston to wall clearance as these modern pistons. They also sit .025" in the hole compared to the Mahle which sit .013" in the hole. Also hundreds of grams lighter. So better quench, my block needed .016" to straighten up. With the .042" compressed Felpro, that gives me .039" piston to head clearance, about perfect. Here are some pics.
Last edited by olds 307 and 403; July 27th, 2021 at 05:24 AM.
Piston dish as said. The new Mahle 4032 forged and coated 10cc dish piston with a 1mm/1mm/2mm ring pack is really nice the Cutlassefi brought to the market. It will give mid 9 to 1 compression with your #6 iron heads and is available in a 4.100" size. That is a 0.043" overbore and size I went with since a couple of cylinders would not clean up at 4.065". The cast replacement pistons will give you 8 to 1 compression at best, very short on compression height. The Speedpro forged are made in India and need twice the piston to wall clearance as these modern pistons. They also sit .025" in the hole compared to the Mahle which sit .013" in the hole. Also hundreds of grams lighter. So better quench, my block needed .016" to straighten up. With the .042" compressed Felpro, that gives me .039" piston to head clearance, about perfect. Here are some pics.
if I get to that point I will have him give me a quote on a set . Are they press in wrist pins? Thanks for the info
To say these pistons sucked getting out is an understatement!
this piston pictured literally came out in two pieces .finally got the crankshaft out it it looks pretty good . I have one final piston left to remove but tonight it’s dinner and drinks ! Been a long week
Location: Colorado Springs Colorado/Thousand Oaks Ca
Posts: 1,721
Originally Posted by BillK
The biggest issue I see is the pitting in the bores. It may or may not clean up when you bore it. Take some 80 grit sand paper and go at one of the cylinder walls till you get to bare metal and then see what it looks like. #3 in your picture looks like the worse one. You cant hurt it and it might give you a better idea if it is worth fooling with.
July 26th, 2021, 06:16 AM
